This invention relates to epoxy resin-based electrical encapsulation compositions.
Epoxy resins are used to encapsulate electrical components such as integrated circuits. The optimum properties for encapsulation resins include high glass transition temperature in the cured state, good crack resistance under soldering and low water adsorption.
Recent developments in the use and packaging of semiconductive elements include surface mounting of such elements. In the surface mounting process, the semiconductive device is immersed in a bath of molten solder and exposed to high temperature. Under these conditions, any moisture in the encapsulating material will expand and cause the encapsulating material to crack.
The currently most widely used epoxy-based encapsulating formulation contains an o-cresol novolac epoxy resin. Such resins have high hydroscopicity (tendency to adsorb water) and poor crack resistance during soldering. Epoxy resins which are derived from the condensation product of phenols and hydroxy benzaldehydes exhibit good thermal stability but tend to have high hydroscopicity and to crack under soldering.
It is therefore an object of the invention to provide an epoxy-based electrical encapsulation formulation which has good thermal stability, low hygroscopicity and good crack resistance under soldering.